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Nov. 2l, 1950 M. D. LxsToN Re 23,295

, MODULATED HEAT RAY DETECTOR Original Filed May 29, 1944 nventor Reissued Nov. 21, 1950 RAT-ENT OPH-ice @MDULTEDHEATFBAY'DETECTGR mistengellarien, Conn., gaesignnr to @Genotorsffnrpnration, fDetroit,.-Mieh., Qa cormesenger;

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Reerring now more speccally@thertofzithere f --fsens'itive vio "the fheat news'fand =Whieh"'may 1Jee"located 'iin -fsome -iffooussing rmeans, .not fshown, forf'eone'entratingf-the '.-i-noidentvrays :onAF the ithermopile. The thermopile is connected by Filmes 111.0 A:interrupter vxmeans lcomprising a movable iarm from the thermopiie is connected to.a'-:eenter1ta.p *.-27onwvfnding 18. ffhefseeorrdaryi24foftheftransfnrmers connected directlyztoaa vacuum-ftube .amplifier 26:.of conventional vform.

@The output offltheamplier s26 `=is connected'zto a zprimary'f of :a second transformer, ithexsee- .fondamyiiifofr Whichdsfconnected through'rtwo'lines 3;-2:'andeswwithsspaoed:eoritacts-S i5 and-respee- Itwelyfofaa serzond interrupter. Themovable inter'.- 26 frnpter armfsorzvibrator All fis, connected through input ',of thetiter'. The viter r output iis -.con 3U :neetedidireetlysto'athird transformerfprimary, :theffsecondaryem hof which isfoonnected-.through dine i521 with stationary :spaced Contact 56 :and ,through fine ,58 Lwith aseeondlspace'd contact. thi-rd svibratory `contact 1262, cooperating with ,eontrerftsafl arr'd Si! is nonn'ected "through linefd =x1vitih=anV indicating-i device or meterf. Thefcenter tap=66aof the .seeondary'zl is likewisesconnected f,through:.1ine iii .with :therneter '268. Af. condenser .12 :.isfeonneotedsaoross the lines and f'i'uatfthe inputzrofxthezmeter.

{Ehe fbasic :operation of fthis 'type `ofssystem 1is substantially the same as thatfdselosedinthe :Sergeant :and .iH'oeper iapplication @above referred ltort-hat -is,1,thatf as the: beamfofinfra -red-:rays 'fails .:Uponithe fthermople 1.14, @the asame will createf'a NeeyasmailowofLdirecteeurrent. Assuoiingathat aefmtaet il@ :for .the .im-oment x'engages stationary cantanti t2 it' wiilbeaobvousthat this current/Will iiiow 'through the lower half of transformer prrimany :118. risvsoon however, as'this1vbrator armature fm leaves toontact I 2 and engages -conftaotddl, the lower haii of -the :primary '-FB -will :beeome ttieenerg1ze`d"fbut'l the upper herir will now 'be :energized Thus =as the lt'-bratory lmember I 0 oscillates'between `the 'itwo ycontacts ft2 and "14,

opposite halves of the winding I 8 will be energized. This induces an alternating current in the secondary Windingl 24 of the transformer of a frequency dependent upon the speed of movement of the armature IU back and forth between |2 and I4.

This alternating current is then amplified by a conventional thermionic tube amplifier 26 and the output thereon is applied to the primary 29 and induces in the secondary 30 4of this second transformer voltage. However, in this output circuit a similar vibrating or oscillating armature d is provided which contacts either stationary contact 36 or 38. This armature is synchronized with armature lil and contacts its respective stationary contacts at exactly the same time. Thus, though current is induced in the complete secondary winding 30, only one-half of the winding is connected inthe output circuit at a time and therefore the current is rectified back to direct current by this method and applied to indicating means or as in this case to the band pass filter. In this manner through the two synchronized breakers and the amplifier small :into the thermopile from some other object nearer than the one which is being located or measured,

they would entirely upset the operation and give erroneous readings. Likewise, if some error crept into the operation of the thermopile through stray currents, additional erroneous indications would be obtained.

I therefore provide a means for modulating or interrupting the beam of light rays which are then detected and amplified as just described, filtering to remove all but the power of the chopping frequency and at a later point synchronously switching the result of the amplification and filtering to provide an amplified direct current attributable only to the desired infra-red source. That is obtained by rotating a ray chopper or intercepter 14 so that it periodically interrupts the flow of infra-red rays from the source to the thermopile once per revolution. This chopper 14 may be mounted upon any suitable rotating shaft 16. Thus the incoming rays will now have a modulating frequency dependent upon the R. P. M. of the light chopper. This is preferably relatively slow. When, therefore, a pulsating direct current is obtained in lines 42 and 48 after being amplified by the amplifier 2G, the band pass filter M is so designed as to reduce the amplitude of the components of frequency other than those which have been generated by the light chopper. We then obtain at the transformer 59 a pulsating current Whose major modulating frequency depends upon the speed of rotation of the chopper. f

In order to reduce this to a direct current which may be read upon the indicating meter,l a further rectifying switch is provided synchronized with the light chopper 14. This switch is the oscillating arm 62 which cooperates with the stationary contacts 5B and 6|). By this action, therefore, the current is again converted to a direct current and a conventional ammeter will read the amount thereof to provide a direct indication of the strength of the infra-red rays impinging upon the thermopile and at the same time D. C. signals un'modulated or those modulated at some other frequencies are converted into A. C.' and cancel sensitive means] out at a direct current indicator; also, A. C. signals of other frequencies passed by the synchronous rectifier likewise'cancel out.

It will be obvious that there are two sets of synchronized means, the first set is the chopper 14 and the vibrating armature 62 which provide and rectify the slow undulating pulse which a1- lows other frequencies to be filtered out and the second set comprising vibrator armatures l0 and 4U synchronized together to create a higher frequency solely for the purpose of amplifying the relatively weak currents flowing and which are rectified before the amplified current is applied to the filter.

[1.A AIn detecting means, a source of rays, sensitivemeans uponwhich the rays are directed to create voltage differences,.means .for periodically interrupting the incident rays interposed between the.source and the sensitive means to modulate the `voltage of the sensitive means at the. frequency. l of interruption, filtering means connected Ato -thesensitive means to pass the modulating frequency but reduce other frequencies that mayhave been introduced and rectifying means synchronizedy with the interrupting means connected to-the filter to convert the .resultant current. to direct current and to pass as A. C. spurious signals from the circuit of the [2. In detecting means, a source of rays, sensi-'- tive means upon which the rays are directed to create voltage differences. means for periodically interrupting the incident rays interposed between the source and the sensitive means to modulate the voltage of the sensitive means at the frequency of interruption, filtering means connected to the sensitive means to pass the modulating frequency but reduce other frequencies that, may have been introduced, rectify/ingr Imeans synchronized -with the interrupting means connected to the filter to convert the resultant current to direct current and to pass as A. C. spurious signals from the circuit of the sensitivemeans andindieating means connected to the rectifier to indicate the outputJ, A

[3. In means for detecting the presence of rays inthe infra-red portion ofthe spectrum, a source of ravs, thermonile means upon which said rays fall, opaque intercepting means capable of internosition between the source and 4the thermonile means, means to-periodically indicatingr means vconnected in turn to the rectifying means] [4. In a detecting apparatus, the combination -of a source of radiantenergy, -a detecting element developing a voltage in response to rays from the source falling thereon, means between the source and element for periodically interruntingr the rays, vanelectronic amplifier confvnected to the elementand amplifying the output therefrom, and a rectifier receiving. the output of mlm the amplieriandeoperatingdinitimed relation to the ,interrupting meanstopass as D. C. thesignal ,introduced-.by the peridic.Linterruptionend to pass as A. C. spurious signals 'from the circuit of the detecting-"elemeritil :min affdetecting apparatus-fthe 'combination of a source offmdlantenereyrfa. detecting yelement developing a Voltage in response to rays from the source falling thereon, means between the source and element for periodically interrupting the rays, an electronic amplifier connected to the element and amplifying the output therefrom, and contactor rectifyng means receiving the output of the amplifier and operating in timed relation to the interrupting means to pass as D. C. the signal introduced by the periodic interruption and to pass as A. C, spurious signals from the circuit of the detecting element] 6. A heat ray detecting system, which comprises a source of infrared rays, a nonselective thermal detector developing voltages in response to radiation from the source falling thereon and greater voltages in response to stray radiation falling thereon and stray thermo-potentials introduced into the system, means between the source and the detector for periodically interrupting the radiation from the source at a loro frequency, a circuit interrupter connected to the thermal detector to periodically interrupt the current therefrom, an amplifier connected to the circuit interrupter and having applied thereto the interrupted current from the thermal detector, a second `circuit interrupter synchronized with the first, connected to the amplifier output to convert the amplified resultant voltage bach to the form of the voltage in the detector output, and a rectifier connected to the second scircuit interrupter and operating in synchronism with the periodically interrupting means for the detecting means to convert the resultant current to direct current and to pass as A. C. spurious signals from the circuit of the detector.

7. In a detecting apparatus, the 'combination of a source of radiant energy, a thermal detecting element developing a voltage in response to rays from the source falling thereon, means between the source and element for periodically interrupting the rays, a circuit interrupter connected to the thermal detector to periodically interrupt the current therefrom, an amplifier connected to the circuit interrupter and having applied thereto the interrupted current from the thermal detector, a second circuit interrupt-er synchronized with the first, connected to the amplifier output to convert the amplified resultant voltage bach to the form of the voltage in the detector output, filtering means connected to the second interrupter output to pass the modulating frequency but attenuate other frequencies that output oftlteenrst Interrupter-rmeuns, a second currenteinterrupter means synchronized ,with-,the .first and connected to theoitput of theelectroric .amplifier means to reconvertthe; amplified .pre- .fdetermine'frequency A.' Ufbafl to D. C,.I1iltering :means connected to fthe. 'second current 'interrupter 1output'to passthe mailula'ting frequency ibut attenuate other "frequencies "that `myay-hzl've Tilman-introduced, a reetif'erto uneted tatheaimfilifier and 'synchronized u'iith "the periodic interrupting means to pass as D. C. desired signals and as A. C. spurious signals from any source, and indicating means connected to the rectifier output.

9. A heat ray detecting system, which comprises a source of infrared rays, a nonselective thermal detector developing D. C. voltages in response to radiation from the source falling thereon and greater voltages in response to stray radiation falling thereon and stray thermo-potentials introduced into the system, means between the source and the detector for periodically interrupting the radiation from the source at a low frequency, a first current interrupter means to convert the D. C. to a predetermined frequency A. C. `connected to the output of the thermal detector, an electronic amplifier means connected to the output of the first interrupter means, a second current interrupter means synchronized with the first and connected to the output of the electronic amplifier means to recouvert the amplified predetermined frequency A. C'. hack to D.C., and a rectifierconnected to the output ofthe second interrupter means and operating in synchronism with the periodically interrupting means for the detecting means to convert the resultant current to direct current and to pass as A. C. spurious signals from the circuit of the detector.

I0. In a detecting apparatus, the combination of a source of radiant energy, a thermal detecting element developing a D. C. voltage in response to rays from the source falling thereon, means between the source and element for periodically interrupting the' rays, a first current interruuter means to convert a D. C. to a predetermined frequency A. C. connected to the outputofthe thermal detector, an electronic amplifier means .connected to the output of the first interrnpter means, a second current intcrrupter means synchronized with the first and connected to the output of the electronic amplifier means to recouvert the amplified predetermined frequency A. C', back to D. C., filtering means connected to the second interrupter output to pass the modulating frequency but attenuate other freauencies that may have been introduced, and a rectifier connected to the filter output and operatina in timed relation to the ray interrupting may have been introduced, and a rectifier concc means t m53 as D- C'- the Sf'mal intloduced by nected to the filter output and operating in timed relation to the ray interrupting means to pass as D. C. the signal introduced by the periodic interruption and to pass as A. C. spurious signals from the circuit of the detecting element.

8. In means for detecting the presence of rays the periodic interruption and to pass as A. C. spurious signals from the circuit of the detecting element.

MAX D. LISTON.

REFERENCES CITED The followinc references are of record in the iile of this patent or the original patent:

UNITED STATES PATENTS Numr Name Date 1,475,583 Hoxie Nov. 27, 1923 1,605,395 De Ybarrondo Nov. 2, 1926 1,901,400 Marrson Mar. 14, 1933 (Other references on following page) 7 UNITED STATES PATENTS FOREIGN PATENTS Number Name Date Number Country Date 1,954,204 Hayes Apr. 10, 1934 671,864 Germany Feb. 17, 1939 2,032,588 Miller Mar. 3, 1936 2,114,293 Gunn Apr. 19, 1938 5 OTHER REFERENCES 2,133,670 schuchmann oct. 13, 1938 Henney. Electron Tubes in Industry, 193'1J pp. 2,269,574 Lidde1 et 9,1 Jan, 13, 1942 448-450, McGraw-H111 Book Co., New York. 2,287,808 Lehde June 30, 1942 2,390,739 Scherbafkoy Dec. 11, 1945 

